The New York City subway, with its passive air exchange system and tunnels too small for active ventilation or air conditioning, have gotten excessively hot this summer:

On Thursday, temperatures inside at least one of the busiest stations reached 40°C—nearly 11°C warmer than the high in Central Park.

The Regional Plan Association, an urban planning think tank for the greater metropolitan area, took a thermometer around the system’s 16 busiest stations, plus a few more for good measure, and shared the data with CityLab. A platform at Union Square Station had the 40°C reading at 1 p.m., which was the hottest they found, although Brooklyn Bridge-City Hall and Columbus Circle weren’t far off at 39°C and 38½°C, at around 10 and 11 a.m., respectively. Twelve out of the 16 busiest stops boiled at or over the 32°C mark in the late morning and early afternoon.

One might think that subway stations would offer crisp respite to sweaty New Yorkers, being underground and all. But you’d be wrong. Heat doesn’t only “rise”—it just diffuses to cooler areas, which can include below-ground spaces. Plus, only a few of the city’s 472 stations are equipped with air conditioning; most rely on a passive ventilation system better known for their Marilyn Monroe moments above ground. This system was built in the days before AC, and the MTA says it’s not possible to squeeze the station-cooling machinery that other metro systems have inside New York’s narrow tunnels. Meanwhile, the units that cool passengers inside cars actually shed heat into the stations as trains pass through.

That onboard air-conditioning can fail, too. The MTA has also seen a rising number of complaints about overheated cars in recent years. In today’s issue of Signal Problems, his indispensable newsletter focused on subway accountability, the journalist Aaron Gordon reports that “about two percent of all subway cars in service on any given day might not have working A/C,” according to the MTA. That means at least 100 cars are roasting passengers on any given day this summer.

Meanwhile, here in Chicago, we're having our 73rd day this year above 27°C, just 10 short of the record. Given the normal number of temperatures that warm between now and October, I think we'll probably set a new one.

David Harper

8/14/2018 6:13:44 AM +00:00 |

Most of the Tube lines in London run in deep-level narrow-bore tunnels, so there are basic physics constraints on fitting air-conditioning units to the rolling stock. An A/C unit works by pumping heat from inside the space it is cooling to outside. In the deep-level Tube system, "outside" is the tunnels and stations. The choice becomes whether you cook your passengers in the trains or on the station platforms. The answer, of course, is to install equipment to move the excess heat from the tunnels and stations to the surface, but that's easier said than done in a system that is a century old. Still, I'm glad I don't live in London any longer. I commuted on the Central Line for six years back in the early 1990s, and that was enough for me.